Fig. 31.—Pupil by iritoectomie. Two incisions. Convergent V (DeWecker).
Fig. 32.—Stenopaic pupil. Single iris incision (DeWecker).
I have already suggested the possibility of Bowman’s paper before the London Congress of 1872 having given origin to DeWecker’s monograph in 1873. This seems quite reasonable when we consider that Bowman proposed two methods of iridotomy, one his double V operation with a rhomboidal pupil (previously quoted), and the other a visual iridotomy or sphincterotomy, by cutting through the pupillary margin with a blunt corneal knife. These two methods are exact prototypes of DeWecker’s proposals. Furthermore, DeWecker was present at the London Congress where he heard Bowman’s paper, and took part in its discussion. In fact, thirteen years later DeWecker acknowledged30 that after considering the objections to Bowman’s method of iridotomy “I addressed myself at that time to the search for an instrument which allows the avoidance of all traction on the iris, and which can be handled through a narrow opening, while exerting its cutting action in a plane parallel to the surface of the cornea, against which the diaphragm of the iris applies itself, after the escape of the aqueous humor. The forceps-scissors having been discovered, it was easy for me to cause to be revived the procedure of Janin, and to make it decisively take rank in modern ocular surgery.”
DeWecker makes only a casual reference to Maunoir’s method, but credits Janin with the original suggestion of the method which he has thus elaborated. Nevertheless, it is quite evident that DeWecker’s method was simply a modification of the one outlined by Maunoir seventy years before. Furthermore, he lays down the same rule that Maunoir first offered: “Always cut parallel to the radiating fibers and perpendicularly to the circular fibers of the iris.”
In reviewing the questions at issue between these two schools of iridotomy, one can not help noticing the constant oscillation from one method to the other as certain advances were made. The method by the knife-needle seemed to possess the advantage of easy accomplishment and less postoperative disturbance, but with the disadvantage that often the pupillary opening was inadequate and promptly reclosed by plastic exudate. On the other hand, the method by the scissors was more difficult of accomplishment, caused more traumatism to the eye, was often complicated by great loss of fluid vitreous, and was frequently followed by severe inflammatory reaction. If, however, it proved successful, the resulting pupil was permanent and sufficiently large for visual purposes. The inclination of all operators seemed to be toward the use of the knife-needle, and it was only necessity that forced them to adopt the more complicated procedure of the open operation with scissors. Von Graefe seemed to recognize this when he referred to the knife-needle incision as “a sub-corneal act which enjoys the immunity of subcutaneous operations.”
The chief advantages of iridotomy by the knife-needle are the ease of incision, the lack of traction on the ciliary body, the freedom from postoperative inflammatory reaction, the avoidance of opening an eyeball which may contain fluid vitreous, the lessening of the tendency to iris hemorrhage from lowered tension, and the avoidance of the nebulous scar which often follows a large corneal incision in old inflammatory eyes. The disadvantages revealed in the method of the knife-needle lay partly in the method and partly in the faulty instruments constructed in that day. Cheselden, Morand, Sharpe and Adams all made the mistake of entering the eye back of the corneoscleral junction, which is so near to the danger zone of the eye. Adams, however, made a two-fold improvement in adding to his operation a sawing movement and in advocating the “most delicate pressure of the instrument” in order to make a free incision. Heuermann was apparently the first to make the puncture through the cornea instead of through the sclera.
The advocates of the knife-needle method long labored under the disadvantage of making a single iris incision, while those who employed the scissors early discovered that a double incision was necessary to success. Although Janin was the originator of the scissors method, Maunoir was the first to deliberately try a triangular flap, which DeWecker later elaborated and made a permanent success. The many disastrous results of the open operation, however, compelled conservative surgeons, like von Graefe, to revert to a study of Cheselden’s method, and to seriously consider the great advantages which a successful iridotomy by the knife-needle method would confer on surgeon and patient alike.
1. Cheselden’s knife-needle (Figs. 3 and 4) was a splendidly designed instrument, but a poorly executed one. The blade was too large (11 mm.) and the shank improperly rounded, so that both aqueous and vitreous were liable to escape through the scleral puncture. This leakage may explain many failures, although the single iris incision was undoubtedly the most serious fault of the method.
2. The iris-scalpel of Adams (Fig. 7) was poorly designed but splendidly executed, the long blade completely filling the wound and thus preventing the escape of any fluid. The cutting edge, however, was too long (15 to 20 mm.), and especially so for the execution of the sawing movement advised by Adams.
3. The double-edged lance-knife (Figs. 5, 12 and 33) employed by Heuermann, Beer and von Graefe, was useful for the long sweeping incision in the iris-membrane which they advocated, but is not adapted for the method which will be described later. The same shaped knife (Fig. 33) with a smaller blade and a longer shank is also used for this purpose, but is likewise too broad, too oval pointed and too much bellied to cut well, while the upper edge is liable to scarify Descemet’s membrane at the same time that the lower edge is executing the incision in the iris tissue.
4. The sickle-shaped knife (Fig. 16) which von Graefe recommends and Galezowski employs, is excellent for making the puncture, but for the go-and-come movement, which Galezowski advises, is not nearly so good as the straight blade with a slight falciform point. It closely resembles the older falciform knife of Scarpa.
5. The knife-needle of Knapp (Fig. 34), which is so generally used for capsulotomy, is unfortunately not well adapted for iridotomy. The point is too oval, the cutting edge is too much bellied, and the blade is too short (5 mm.). It will not easily puncture a dense iris-membrane, and the long sawing incision can not be well executed, because the short blade either persists in slipping out of the iris incision or else allows the membrane to ride up on the shank, in either case interfering with the completion of the operation.
6. Sichel’s iridotome (Fig. 35) closely resembles Knapp’s knife-needle, and although specially designed for this purpose, has the same faults, an oval point and a bellied edge. On the other hand, the blade is too long (11 mm.) to be easily manipulated in the anterior chamber.
7. The Hays knife-needle (Fig. 36), as suggested in the early part of this paper, has the same general shape as Cheselden’s instrument, although much smaller. It was devised by Dr. Isaac Hays, an early surgeon of the Wills Hospital, and, although not well known to the profession at large, has been in constant use by the staff of that hospital for more than half a century. I may be pardoned for briefly quoting the original description of the instrument as published by Hays31 in 1855:
“This instrument from the point to the head, near the handle (a to b, Fig. 36), is six-tenths of an inch, its cutting edge (a to c) is nearly four-tenths of an inch. The back is straight to near the point, where it is truncated so as to make the point stronger, but at the same time leaving it very acute, and the edge of this truncated portion of the back is made to cut. The remainder of the back is simply rounded off. The cutting edge is perfectly straight and is made to cut up to the part where the instrument becomes round, c. This portion requires to be carefully constructed, so that as the instrument enters the eye it shall fill up the incision, and thus prevent the escape of the aqueous humor.”
Fig. 4.—Cheselden’s knife-needle (after Sharpe).
Fig. 37.—Ziegler’s model of knife-needle.
Fig. 36.—Hays’ knife-needle, exact size and enlarged (Hays).
Fig. 16.—Sickle-shaped knife, Aiguille-à-serpette (Galezowski).
Fig. 35.—Sichel’s iridotome (after Meyer).
Fig. 34.—Knapp’s knife-needle.
Fig. 7.—Adams’ iris-scalpel; large and small size.
Fig. 33.—Double edged lance-knife (modern model).
Fig. 5.—Double edged lance-knife (Beer).
Fig. 12.—Iris-knife (Walton, after Beer).
The Various Knife-Needles and Iris-Knives Mentioned in the Text.
(Grouped together for study and comparison.)
8. The knife-needle, which I invariably use, is a modified pattern of that devised by Hays. The form of this instrument lies midway between the falciform knife and the bistoury, and possesses the advantages of both. It has a very delicate point which punctures easily, and an excellent cutting edge of sufficient length (7 mm.). If the shank is properly rounded it can be used with a sawing motion, sliding backward and forward through the corneal puncture without injuring the cornea, and without allowing the aqueous to escape. To accomplish this the more easily, the shank has been made 4 mm. longer than the original model. This instrument, therefore, seems to meet all the requirements of a perfect iris-knife, viz., a falciform point which makes the best puncture, a straight edged blade which makes the best incision, and a cutting edge 7 mm. long, which is the best length for properly executing the sawing movement. My model32 of knife-needle (Fig. 37) resembles Cheselden’s knife, as shown by Sharpe (Fig. 4), even more closely than the original pattern of Hays does.
Fig. 37.—Ziegler’s model of knife-needle.
1. A good knife-needle must be carefully selected. We have already concluded that the modified Hays knife-needle is the best model for this purpose. The knife-needle must, of course, have a well sharpened point and edge.
2. The character of the incision in the iris-membrane is of vital importance. It should be a double incision. Guérin, Maunoir, DeWecker and Galezowski recognized this. Guérin made a crucial incision, Maunoir and DeWecker adopted the triangular flap, while Galezowski advocated the T-shaped cut. Our choice is the V-shaped incision, which is undoubtedly the only one that will cut through all the iritic fibers in such a way as to give us the greatest retraction of the membrane.
3. Absolutely no pressure should be made in cutting with the knife-needle. This must be recognized as the main secret of success, whether you are incising a dense, felt-like iris-membrane, or a thin filmy capsule. If this rule is observed all traction on the ciliary body will be avoided.
4. The knife-needle should slide backward and forward through the corneal puncture with a gentle sawing movement.
5. The corneal puncture and membrane counter-puncture should be far enough apart to make the corneal puncture a good fulcrum for the delicate leverage necessary in executing the iris incision.
6. The knife-needle should be so manipulated that no aqueous shall be lost, as this accident may prevent the completion of the operation, and may increase the tendency to iris hemorrhage by lowering the ocular tension.
7. Every incision should be made a thoroughly clean cut, and all tearing of the tissues should be avoided.
8. The most perfect artificial illumination should be secured, either by an electric photophore or a condensing lens, as both iridotomy and capsulotomy require constant and close inspection of the operative field.
The method of V-shaped iridotomy, performed by me with my modified Hays knife-needle, may be described as follows:
First Stage.—With the blade turned on the flat, the knife-needle is entered at the corneo-scleral junction, or through the upper part of the cornea (Fig. 38), and passed completely across the anterior chamber to within 3 millimeters33 of the apparent iris periphery. The knife is then turned edge downward, and carried 3 millimeters to the left of the vertical plane (Fig. 39).
Second Stage.—The point is now allowed to rest on the iris-membrane, and with a dart-like thrust the membrane is pierced. Then without making pressure on the tissue to be cut, the knife is drawn gently up and down with a saw-like motion, until the incision has been carried through the iris tissue from the point of the membrane puncture to just beneath the point of the corneal puncture. This movement is made wholly in a line with the axis of the knife, the shank passing to and fro through the corneal puncture, and the loss of any aqueous being carefully avoided in the manipulation.
Fig. 38.—Author’s V-shaped iridotomy. Knife-needle entered through cornea.
Fig. 39.—Author’s method. Plan of first incision.
Fig. 40.—First incision completed. Plan of second incision.
Fig. 41.—Pupil resulting from V-shaped iridotomy.
Third Stage.—The pressure of the vitreous will now cause the edges of the incision to immediately bulge open into a long oval (Fig. 40) through which the knife-blade is raised upward, until above the iris-membrane, and then swung across the anterior chamber to a corresponding point on the right of the vertical plane, which, owing to the disturbance in the relation of the parts made by the first cut, is now somewhat displaced and the second puncture must be made at least 1 millimeter farther over, i. e., 4 millimeters to the right of the vertical plane (Fig. 40).
Fourth Stage.—With the knife point again resting on the membrane, a second puncture is made by the same quick thrust, and the incision rapidly carried forward by the sawing movement to meet the extremity of the first incision, at the apex of the triangle, thus making a converging V-shaped cut (Fig. 41). Care must be taken at this point that the pressure of the knife-edge on the tissue shall be most gentle, and that the second incision shall terminate a trifle inside the extremity of the first, in order that the last fiber may be severed and thus allow the apex of the flap to fall down behind the lower part of the iris-membrane. If the flap does not roll back of its own accord it may be pushed downward with the point of the knife. When the operation is completed the knife is again turned on the flat and quickly withdrawn.
The most fruitful sources of failure are, first, a poorly sharpened knife-needle; second, a badly planned incision; third, inability to sever the apex of the triangle; fourth, the early loss of aqueous; fifth, too heavy pressure with the knife-edge, and sixth, rocking or rotating the knife backward instead of making the sawing movement. All of these can easily be avoided, if the surgeon will only exercise care and good judgment.
In an occasional case, the iris-membrane may be so stiff that the apex of the flap will not retract. If the apex can not be pushed down by the tip of the knife turn the blade on the flat, puncture the base of the flap by a quick thrust, and with a sawing motion cut across its fibers so that it will fall back as though hinged; or, if positive that the vitreous is not fluid, introduce a keratome in the cornea below, draw out the triangular tongue, cut it off with the iris scissors, and dress back the base with a silver spatula.
It is possible that the capsule, or iris tissue, may lose its anchorage. In that event we must either reverse the procedure by entering the knife-needle below, and cut from above downward, or else pass a second knife-needle through the loosened edge of the membrane to fix it, and then proceed with the usual method.
Occasionally, the apex of the triangular flap will hold fast, because the last fiber of tissue has not been severed. If the leverage is too short to incise it from above, withdraw the knife-needle and reintroduce it far enough from the apex to secure the proper leverage, and again incise it gently, until it falls back.
Traction on the ciliary processes, accidental puncture of the ciliary body, or the tearing of the membrane from its ciliary attachment may all set up iridocyclitis or glaucoma, and should therefore be avoided. As tense capsular bands are liable to engender a similar condition they should be incised. If any of these traction bands should remain in the edge of the coloboma, we may enter the knife behind them and gently saw through into the already cleared pupil, before withdrawing the knife.
Fig. 42, (Case 1).—Iridotomy in a stiff iris-membrane (author’s original case).
I will briefly cite a few examples of the V-shaped operation, two that were my first efforts, and two that were recent cases. They were all of the class that are often abandoned as hopeless; hence the visual result is far below the operative success.
Case 1.—History.—F. M., aged 65 years. O. D. complete membranous occlusion of pupil from iridocyclitis, following cataract extraction. The iris and capsule are tensely drawn up toward the ciliary border. Light perception and projection good. Several efforts have been made to incise the membrane, but without success. Admitted to Wills Hospital by the late Dr. Goodman, through whose courtesy I operated.
Operation.—On Jan. 15, 1889, I made two long incisions, almost crucial, and extending beyond the apex of the V, resulting in a W-shaped pupil, on account of the stiff iris membrane (Fig. 42). With S. + 10 D. he saw 20/50.
Case 2.—History.—J. S., aged 30 years. O. S. injured and enucleated. O. D. sympathetic inflammation, chorioidal cataract; three discissions and one iridectomy, down and in. Membranous occlusion of pupil. I first saw him in 1888 while house surgeon at the Wills Hospital, where iridotomy was skilfully performed nine times by one of the surgeons, the methods being varied and ingenious, but without success, as the incision was invariably closed by plastic exudate. My interest in this series of operations first drew my attention to the subject of iridotomy, and stimulated me to develop the method I have here submitted and which I first tried in Case 1.
One year later this patient came to my clinic at St. Joseph’s Hospital. Iris was discolored, capsule thickened and visible through the coloboma, down and in; areas of scleral thinning, with pigmented chorioid showing through. T—3. Light perception good, projection only fair.
Operation.—On June 17, 1889, I made a V-shaped iridotomy along the outlines of the former iridectomy. The membrane freely opened up into a triangular or pear-shaped pupil (Fig. 43), which proved permanent, but was only useful for quantitative vision, about 5/200. No further test could be made because the disorganized vitreous was filled with floating masses. I have seen him within a year, going about and earning his living. From an operative standpoint I have always considered this early effort one of my most successful cases, chiefly because of the great density of the iris-membrane and the lowered tension of the eyeball.
Fig. 43, (Case 2).—Iridotomy in a soft eyeball, with dense iris-membrane.
Case 3.—History.—Mrs. A. D., aged 45 years. O. D. iridectomy for glaucoma seven years ago. O. S. iridectomy two years ago by another surgeon, at which time there occurred slight incarceration of iris, followed by sympathetic ophthalmitis in O. D. The severe iridochorioiditis resulted in cataract and some shrinkage of globe. The cataracts were extracted from both eyes in 1907, followed by dense opacity of cornea above, iris bombé, shallow anterior chamber, T—2. Here was a soft, distensible, iris tissue with shallow anterior chamber and greatly lowered tension of the eyeball, constituting one of the most difficult conditions to operate on.
Operation.—On May 13, 1907, the eyes being quiet, and light perception and projection fair, V-shaped iridotomy was performed on both eyes. The leucomatous areas in the upper part of cornea necessitated making the pupil below. In O. D. the pupil opened up beautifully (Fig. 44), but in O. S. a tag of iris hung fast (Fig. 45) and was again incised two months later. The artist has illustrated the remaining portion of this tag very well. As soon as the iris tissue was incised it retracted, making the pupils larger than the area of incision. The test for glasses, nearly a year later, March 15, 1908, yielded the following result:
O. D. S + 13 D ⁐ C + 4.75 D ax. 105° = 20/40.
O. D. S + 13 D ⁐ C + 3 D ax. 65° = 20/40.
Add
O. D. S + 4 D = J. 10.
O. S. S + 4 D = J. 10.
These were ordered in biconvex torics. She had worn glasses for a year, but claims vision is much better with the new ones. This seems like an excellent result when we consider that these eyes had passed through glaucoma, iridochorioiditis and cataract, followed by membranous occlusion of pupil, lowered tension and fluid vitreous. The high hyperopia and astigmatism show the phthisical condition of each globe. There is marked cupping of both nerve heads and the fields are contracted.
Fig. 44, (Case 3).—Iridotomy in a soft eyeball, with thin membrane and iris bombé.
Fig. 45, (Case 3).—Iridotomy showing apex of iris flap after incision through adherent fibers.
Case 4.—History.—Mrs. B. M., aged 64 years. O. S. struck by a stone in childhood, destroying vision. Dense leucoma above, chorioidal cataract, calcareous deposit; exclusion of pupil. T—1. Lpc. good. Lpj. fair. O. D. recurrent attacks of inflammation for seven years, posterior synechiæ and cataract. Counts fingers at 6 inches. Extraction with iridectomy, both eyes, in 1907. Site of incision has become densely leucomatous. O. D. shows capsular area above, iris drawn up. O. S. complete membranous occlusion of pupil.
Operation.—Oct. 7, 1907, V-shaped incision was executed entirely in the iris tissue of O. D., the pupil spreading out into an ovoid shape (Fig. 46), leaving area of capsule and small band of iris above. O. S. was operated on Jan, 13, 1908, by the same method, the resulting pupil being almost round (Fig. 47) owing to the resilient iris tissue.
The test for glasses, March 10, 1908, gave the following result:
O. D. S + 12 D ⁐ C + 1.25 D ax. 135° = 20/50.
O. S. S + 12 D ⁐ C + 1.25 D ax. 135° = 20/70.
Add
O. D. S + 5 D = J. 6.
O. S. S + 5 D = J. 12.
These were ordered in biconvex torics, which she now wears with great comfort. It is worth noting that O. S. still retained good visual acuity, although blinded by an injury nearly fifty years before.
Fig. 46, (Case 4).—Irido-capsulotomy, with band of iris, and capsule in coloboma above.
Fig. 47, (Case 4).—Iridotomy with round central pupil in a resilient iris-membrane.
The application of the V-shaped method to capsulotomy shows an even greater field of usefulness, as this method is par excellence the best way of incising a delicate secondary capsular cataract. This should be done under artificial illumination. The pupil should be dilated, as the area of incision is necessarily smaller than in iridotomy, and unnecessary wounding of the iris should be avoided. The proposed capsular opening must be so calculated as to fall within the area of the undilated pupil, or partly within the coloboma if an iridectomy has been previously performed.
Fig. 48.—Author’s Vshaped capsulotomy. Plan of first incision.
Fig. 49.—First incision completed. Plan of second incision.
Fig 50.—Pupil resulting from V-shaped capsulotomy.
The knife-needle is entered at the upper corneal margin, passed across the anterior chamber to a point 2 mm. to the left of the vertical plane (Fig. 48), the capsule punctured by a quick thrust, and the saw-like incision carried from below upward, as in iridotomy. The knife is then raised up above the capsule and swung 3 mm. to the right of the vertical plane (Fig. 49), the capsule is again punctured, and a duplicate incision carried up to join the first, at the apex of the converging V (Fig. 50).
Where the pupillary margin is adherent to the underlying capsule, or the pupillary space is too small, it may be necessary to start the incision in the iris tissue, a little below the pupil, and then cut upward until the knife emerges into the pupillary area, thus making an irido-capsulotomy. The soft iris tissue is easily incised if no pressure is made with the knife, and the sawing motion is maintained.
Postoperative inflammatory reaction is infrequent, but if it should occur the usual antiphlogistic treatment of atropin, calomel, ice-pads and leeching should be actively instituted and continued until the eye is absolutely quiet. The operation itself is frequently an antiphlogistic measure, because it relieves iris-tension and traction on the ciliary body. The usual compress of gauze and cotton, covered with a Liebreich patch, may be applied to the eye for the first twenty-four hours and rest in bed enjoined for that period.
We have carefully reviewed the history of iridotomy for nearly two centuries, and noted how the pendulum has swung from knife-needle to scissors, and back again. We have learned that Cheselden, the father of iridotomy, originated the method of incision by the knife-needle, which Heuermann modified, and Adams later revived and improved. We have seen how Janin abandoned this procedure and originated the scissors method, which Maunoir greatly improved and caused to hold sway for more than half a century. We have been deeply impressed by the fact that the mature, judicial mind of von Graefe led him to abandon the scissors and revert to the knife-needle method. We have seen how, soon after his death, the great influence of De Wecker had swerved the thought of the ophthalmic world back to the adoption of the scissors method in a greatly improved form.
Whether I have succeeded in citing sufficient facts and arguments to establish my thesis in favor of the knife-needle, or not, I nevertheless submit to the profession my V-shaped method of iridotomy and capsulotomy with a confidence born of twenty years’ successful experience in its use, and with the hope that it may prove equally efficient in the hands of others who will take pains to study and understand the method, and who may have the patience to put it in practice.
1 Read in the Section on Ophthalmology of the American Medical Association, at the Fifty-ninth Annual Session, held at Chicago, June, 1908.
2 Wagner, Karl Wilhelm Ulrich: Inaugural Thesis, Göttingen, 1818. He invented the designation iridotomia, which he formed from the original Greek, ἶρις, ἶριδος (the iris) and τομή (cut).
3 Cheselden, William: Philosophical Transactions, London, 1728, xxxv, p. 451.
4 Ibid, abridged, vii, pl. v, Figures 2, 3 and 5.
5 Sharpe, Samuel: A Treatise on the Operations of Surgery, London, 1739, p. 169.
6 Adams, Sir William: Practical Observations on Ectropium, Artificial Pupil and Cataract, London, 1812, p. 37 et seq.
7 Guthrie, G. J.: Operative Surgery of the Eye, London, 1830, p. 428.
8 Histoire et Mémoires de l’Académie Royale de Chirurgie, Paris, 1757, iii, p. 115.
9 Huguier, Pierre Charles: Des Opérations de Pupille Artificielle, Paris, 1841.
10 Heuermann, Georg: Abhandlung der Vornemsten Chirurgischen Operationen, Copenhagen and Leipzig, 1756, ii, p. 493.
11 Janin, Jean: Mémoires et Observations sur L’Oeil, Lyon 1772, p. 191.
12 Guérin, M.: Maladies des Yeux, Lyon 1769, p. 235.
13 Beer, Georg Joseph: Lehre der Augenkrankheiten, Wien, 1792, ii, p. 12.
14 Beer, Georg Joseph: Ansicht der Künstlichen Pupillen-Bildung, Wien, 1805, p. 105.
15 Adams, Sir William: A Treatise on Artificial Pupil, London, 1819, p. 34, et seq.
16 Scarpa, Antonio: Trattato Delle Principali Malattie Degli Occhi, Ed. quinta, l’avia, 1816, translated by James Briggs, London, 1818, p. 373.
17 Edin. Med. and Surg. Jour., No. 58.
18 Walton, H. Haynes: The Surgical Diseases of the Eye, London, 1861, p. 604.
19 Meyer, Edouard: Traité Pratique des Maladies des Yeux, Paris, 1880, translated by Freeland Fergus, Philadelphia, 1887, p. 396.
20 Klinische Monatsblätter für Augenheilkunde, 1869, p. 431.
21 Galezowski, Xavier: Maladies des Yeux, 2d. ed., Paris, 1875, p. 401, and 3rd. ed., Paris, 1888, p. 384.
22 A brief description of the author’s method, written by him, was first published in de Schweinitz on Diseases of the Eye, Philadelphia, 2nd. ed., 1896, p. 607.
23 Wenzel, Baron de: Traité de la Cataracte, Paris, 1786, translated by James Ware, London, 1805, ii, p. 256.
24 Maunoir, Jean Pierre: Mémoires sur l’Organisation de l’Iris, et l’Opération de la Pupille Artificielle, Paris, 1812.
25 Medico-Chir. Trans., London, 1816, vii, p. 301, and ix, p. 382.
26 Mackenzie, William: Diseases of the Eye, 3rd. ed., London, 1840, p. 746, American edition, edited by Hewson, Philadelphia, 1855, p. 815.
27 Lawrence, Sir William: Diseases of the Eye, American edition, edited by Hays, Philadelphia, 1854, p. 478.
28 Transactions, Fourth Int. Ophth. Cong., London, 1872, p. 179.
29 De Wecker, Louis: Annales d’Oculistique, Sept., 1873, p. 123, et seq.
30 DeWecker et Landolt: Traité Complet d’Ophtalmologie, Paris, 1886, ii, p. 393.
31 Amer. Jour. of the Med. Sciences, July, 1855, p. 82.
32 This knife-needle has been carefully made for me by Luer, Paris, and by Ferguson, Philadelphia.
33 Compare with millimeter scale beneath each diagram.